We argue that designing overlay services to independently probe the Internet--with the goal of making informed application-specific routing decisions--is an untenable strategy. Instead, we propose a shared routing underlay that overlay services query. We posit that this underlay must adhere to two high-level principles. First, it must take cost (in terms of network probes) into account. Second, it must be layered so that specialized routing services can be built from a set of basic primitives… CONTINUE READING